a) Field of the Invention
The invention relates to the detection and distinguishing of shelf-forming supports in cassettes and disk-shaped objects deposited thereon by displacement of the supports and objects together relative to a measurement plane in the direction of shelves that are located one above the other, wherein end sides of the supports and objects successively pass through bundles of measurement beams, wherein different types of supports are distinguished from one another by an offset arrangement in the measurement plane vertically to the measurement beam bundles.
b) Description of the Related Art `Technical solutions of the kind mentioned above are applicable in the fabrication of integrated circuits, especially for handling tasks, and are known, for example, from DE 195 35 871 A1.
In the fabrication of integrated circuits, disk-shaped objects such as templates or masks and semiconductor wafers must be transported between different machining steps to individual machining devices. For this purpose, the objects are accommodated in cassettes which, because of cleanroom requirements, are usually enclosed by transport containers. In order to charge the machining devices, the cassettes are unloaded from the transport containers by suitable means and the disk-shaped objects are removed and put back again by a handling device. For this purpose, it is necessary to detect the position of a shelf on which the object is deposited as well as the occupation of a shelf by an object.
Known detection systems are basically distinguished according to two different types. In a first method (mapping), the geometric dimensions of the cassette, especially the distance between shelves, are assumed to be known. If the position of a shelf is aligned with respect to a reference plane of the handling system, the positions of all of the other shelves can be determined and approached by computation. A light barrier determines if a shelf is occupied.
A second method (indexing) includes in the detection possible dimensional deviations of the cassettes due to manufacturing tolerances or deformations. The position of the shelves and objects with respect to a reference plane is exactly determined by means of a sensor system.
It is known from DE 195 35 871 A1, to distinguish types of mask cassettes with a reflection coupler at the same time that shelves and objects are detected. Since the light beam of the reflection coupler strikes either the mask support (6xe2x80x3 cassette) or the crosspiece (5xe2x80x3 cassette), there are differences in the duration of the high level during the movement of the cassette in the vertical direction. With respect to the 6xe2x80x3 cassette, the position of the mask support relative to a reference plane can be determined by a combination of path measurement and determination of the time of the high-low transition of the reflection coupler. In the case of a 5xe2x80x3 cassette, it is necessary that the difference in height between the mask support and the crosspiece is included in the calculation. The presence of objects is detected by positioning a light beam bundle of a light barrier diagonally through the cassette.
It is disadvantageous that dimensional differences usually occurring in the cassettes result in an unrecoverable falsification of the determination of position and in a reduced reliability of detection in distinguishing between types of cassettes.
Therefore, it is the primary object of the invention to increase accuracy in the determination of the position of shelves and objects as well as the reliability of detection in distinguishing between cassette types without a disruptive influence being exerted on the objects by the inserted protective supports.
According to the invention, this object is met by a device for detecting and distinguishing between shelf-forming supports in cassettes and disk-shaped objects deposited thereon by displacement of supports and objects together relative to a measurement plane in the direction of shelves located one above the other, in which end sides of the supports and objects successively pass through bundles of measurement beams, wherein different types of supports are distinguished from one another by an offset arrangement in the measurement plane vertical to the measurement beam bundles. Each of the measurement beam bundles is situated in the region of only one type of support, wherein the extension of the end sides of the supports in the measurement plane is completely detected by the measurement beam bundles.
It is especially advantageous when the measurement beam bundles have a substantially rectangular cross section whose extension in the measurement plane at least corresponds to that of the end sides of the supports and, vertical to the measurement plane, is smaller than the thickness of the objects.
Due to the fact that the measurement beam bundle extends to a sufficient degree in the measurement plane vertical to the beam direction, the light beam detects even a small deviation in position and differences in size of the supports in this direction. The limiting of the vertical dimension of the light beam ensures steep edges of the measurement signal during the passage of the cassette and ensures that the position of the supports and objects are accurately determined. Single-cassettes and multi-cassettes are distinguished by detecting the number of supports and objects.
In a first variant, the measurement beam bundles are directed parallel to one another, are arranged in the region of a wall of the cassette and are at a distance from one another corresponding to the degree of offset.
In a second variant, at least one of the measurement beam bundles is arranged in the region of a wall serving as a carrier for each of the supports, wherein these measurement beam bundles are directed parallel to one another.
The measurement beam bundles are advantageously arranged as laser light barriers whose radiation sources and receivers are accommodated in a frame through which the cassette passes in a vertical movement so as to be aligned with the frame.
A pair of columns serves as a carrier for the frame, wherein the columns are arranged at a distance from one another so as to form an air passage, wherein a drive for an elevator for the vertical movement of the cassette is accommodated in a column.
A further object of the invention is a method for detecting and distinguishing between shelf-forming supports in cassettes and disk-shaped objects deposited thereon. The method is based on the evaluation of signals which are formed by an interruption of measurement beam bundles resulting from displacement of the supports and objects together relative to a measurement plane in the direction of shelves located one above the other, in which end sides of the supports and objects successively pass through measurement beam bundles, wherein different types of supports can be distinguished through an offset arrangement in the measurement plane vertical to the measurement beam bundles. The signals of all of the measurement beam bundles, each of which is situated in the region of only one type of support and completely detects the extension of the end sides of the supports in the measurement plane, are evaluated simultaneously and in correlation with one another.
The invention will be explained more fully hereinafter with reference to the schematic drawing.